Controlled thread brake

ABSTRACT

A controlled thread brake for braking a weft thread ( 10 ) in a weaving machine is presented which comprises a brake band ( 3 ) and a brake body ( 2 ), with the thread brake ( 1 ) additionally comprising an electromagnet ( 6 ) and a rotatable or rocking lever ( 4 ) which can be moved by means of the electromagnet. The lever ( 4 ) is connected to the brake band ( 3 ) so that a pulling force can be exerted in the longitudinal direction of the brake band by means of the electromagnet ( 6 ) in order to be able to press the latter against the brake body ( 2 ) for braking the weft thread.

This application claims the priority of European patent application No.06405031.3, dated Jan. 24, 2006, the disclosure of which is incorporatedherein by reference.

The invention relates to a controlled thread brake for braking a weftthread in a weaving machine in accordance with the preamble of claim 1and to a weaving machine with a thread brake of this kind.

In weaving machines a thread brake is usually provided between thesupply bobbins for the weft thread and the shed in order to brake theweft thread at the end of the weft insertion. More recent weavingmachines are provided with controlled thread brakes which permit theweft thread to be braked during any desired phase of the weft insertion.The document EP 0 475 892 A1 discloses a thread brake of this kind witha brake band and a movable brake body which is connected to a settingmotor in such a manner that the rotational movement of the setting motoris converted to a stroke movement of the brake body. In this manner itis possible to control both the time point of the application of thebrake and the braking force which is exerted on the weft thread via thesetting motor. A disadvantage of the thread brake which is disclosed inEP 0 475 892 A1 is that it is slow in comparison with the duration ofthe individual phases of the weft insertion, i.e. that the brakingaction takes place only with a delay of typically 30 ms or more when acontrol signal is applied to the setting motor. A regulation of thebraking as a result of the current weft data is thus not possible or isat least made considerably more difficult at higher weft insertionrates. A further disadvantage is represented by the comparatively highmanufacturing costs of this thread brake.

The object of the invention is to make available a controlled threadbrake for braking a weft thread in a weaving machine and a weavingmachine with a thread brake of this kind which has a shorter reactiontime than the above described state of the art and which can bemanufactured comparatively economically.

This object is satisfied in accordance with the invention by the threadbrake which is defined in claim 1 and by the weaving machine which isdefined in claim 10.

The controlled thread brake in accordance with the present invention forbraking a weft thread in a weaving machine includes a brake band, forexample a yielding or flexible brake band, and a brake body which canfor example be stationary and/or arranged in a fixed position. Inaddition the thread brake comprises an electromagnet and a rotatable orrocking lever which can be moved by means of the electromagnet and whichis operationally connected to the brake band in order to be able toexert a pulling force in the longitudinal direction of the brake bandand in order to place the latter or press the latter against the brakebody for braking the weft thread. In an advantageous variant the threadbrake comprises two or more brake bodies, and in a further advantageousvariant the brake body or bodies are provided with a rounded off formand/or are formed as passive braking members.

The brake band can be connected firmly or elastically to a holder at afirst securing point, for example on one side of the brake band and,with a spacing from it in the longitudinal direction, for example onother side, be firmly or elastically connected to the lever. In anadvantageous embodiment the thread brake comprises a spring element forreleasing the thread brake, for example a tension or compression spring,which acts on the lever and/or a leg spring at the point of rotation ofthe lever. The brake band can optionally also be provided with a biastension so that it acts as a spring element for releasing the threadbrake.

The lever is optionally straight or angled. The point of rotation of thelever can, for example, be arranged between the brake band and theelectromagnet or to one side on the side of the brake band or of theelectromagnet. In an advantageous variant the lever is arrangedsubstantially at right angles to the brake band.

In an advantageous embodiment an armature is provided at the lever ofthe electromagnet, said armature containing a ferromagnetic or permanentmagnetic material, for example in that the lever or a part of it isformed as an armature. If required, the thread brake can comprise atleast one second electromagnet, by means of which the lever and/or thebrake band can be moved and which for example can be used as a releasemagnet and/or to assist the first electromagnet. In a furtheradvantageous embodiment the electromagnet has a U-shaped core or theelectromagnet is formed as a pot magnet, with the magnetic field passingthrough the armature.

In a further advantageous embodiment an air gap is provided between thearmature and the electromagnet or electromagnets during the braking. Inthis way it is possible to set the braking force during the braking viathe current which flows through the electromagnet.

Furthermore, the invention comprises a weaving machine with at least onethread brake in accordance with any one of the above describedembodiments.

The thread brake in accordance with the invention is a rapid reactionthread brake which is particularly suited for rapidly running weavingmachines with weft insertion speeds of for example 500 insertions/min.and higher. The paths which are travelled by the moving parts can bekept short, for example 1 mm or less, so that the reaction time that canbe achieved is less than 10 ms. Furthermore, it is possible to controlthe braking force during the braking via the current flowing through theelectromagnet, with the braking force being nearly proportional to thecurrent. This means that the thread brake in accordance with theinvention enables a regulation of the braking as a result of thecurrently determined weft data, in particular also in rapidly runningweaving machines. Also advantageous is its large adjustable brakingforce range, which permits its use in practically the entire yarnspectrum, from fine to coarse yarns. Moreover, the thread brake inaccordance with the invention has a useful self cleaning effect if thebrake band is vented by 1 to 2 mm so that the brake band slaps againstthe brake body when the brake is applied. A further advantage isrepresented by the comparatively favorable manufacturing costs of thedescribed thread brake and the simple and economical control.

The above description of embodiments serves merely as an example.Further advantageous embodiments result from the independent claims andthe drawings. Moreover, in the context of the present invention,individual features from the described or illustrated embodiments andvariants can also be combined with one another in order to form newembodiments.

The invention will be explained in the following in more detail withreference to the exemplary embodiment and with reference to thedrawings. Shown are:

FIG. 1 a perspective view of an exemplary embodiment of a thread brakein accordance with the present invention,

FIG. 2 a side view of the same exemplary embodiment,

FIG. 3A a side view of a second exemplary embodiment of a thread brakein accordance with the present invention during the braking, and

FIG. 3B a side view of the exemplary embodiment which is shown in FIG.3A with released thread brake.

FIG. 1 shows a perspective view and FIG. 2 a side view of an exemplaryembodiment of a thread brake in accordance with the present invention.The illustrated thread brake 1 for braking a weft thread 10 in a weavingmachine comprises a brake band 3, which can for example be designed as aflexible and/or resilient band, e.g. as a steel band, and a brake body2, which is preferably provided with an abrasion resistant surface, forexample with a ceramic plate on the upper side or a coating of a ceramicmaterial or of hard chromium. In addition the thread brake 1 of theexemplary embodiment comprises an electromagnet 6 and a rotatable orrocking lever 4 which can be moved by means of the electromagnet andwhich is actively connected to the brake band 3 in order to be able toexert a pulling force in the longitudinal direction of the brake bandand to place the latter against the brake body 2 for braking the weftthread 10. Of course two or more brake bodies can also be provided. Thebrake body or bodies are advantageously formed as passive brakeelements.

The brake band can be firmly or elastically connected to a holder 8 at afirst securing point, for example at one end of the brake band and,spaced in the longitudinal direction, firmly or elastically connected tothe lever 4 at a second securing point, in particular at the other end.In an advantageous embodiment the thread brake comprises a springelement in order to be able to release the thread brake when the currentis switched off, for example a tension or compression spring which actson the lever and/or a leg spring at the point of rotation of the lever.The brake band can optionally also be provided with a bias tension sothat it is effective as a spring element to release the thread brake. Inthe exemplary embodiment which is shown in FIGS. 1 and 2 the brake bandis deflected slightly by the brake body 2, so that it is placed againstthe brake body 2 if the electromagnet 6 exerts a force via the lever 4in the longitudinal direction of the brake band and a weft thread 10which is inserted between the brake band and the brake body is clamped.

The lever 4 can, as is shown in FIGS. 1 and 2, be straight and the pointof rotation of the lever can be arranged between the brake band and theelectromagnet. It is however also possible to provide angled leversand/or to arrange the point of rotation to one side on the side of thebrake band or of the electromagnet. In the illustrated exemplaryembodiment the lever 4 is arranged substantially at right angles to thebrake band 3 and the latter is secured to the lever.

In an advantageous embodiment an armature 5 of the electromagnet 6 isprovided at the lever 4, for example in that the lever or a part of itis formed as an armature. The armature or the part 5 of the lever whichis formed as an armature expediently contains a magnetically activeregion of a ferromagnetic or permanent magnetic material, for example asoft magnetic steel or, in the case of a permanent magnetic material,e.g. of ALNICO. If a permanent magnetic material is provided in thearmature the electromagnet can also be used for the release of the brakeband through reversal of the current flow. The electromagnetadvantageously has a U-shaped core or the electromagnet isadvantageously formed as a pot magnet, with the magnetic circuit beingclosed by the armature on excitation of the electromagnet with theexception of an air gap.

FIGS. 1 and 2 show the thread brake 1 during the braking; i.e. theelectromagnet stretches the brake band 3 via the lever 4 so that it liesin contact with the brake body 2, and the weft thread 10 is clampedbetween the brake band and the brake body. In the illustrated exemplaryembodiment an air gap is present between the armature 5 and theelectromagnet 6 during the braking. In this way it is possible to setthe braking force during the braking via the current flowing through theelectromagnet, with the braking force being approximately proportionalto the current.

FIG. 3A shows a side view of a second exemplary embodiment of a threadbrake in accordance with the present invention during the braking. Thethread brake which is shown in FIG. 3A differs from that shown in FIGS.1 and 2 only through a second electromagnet 6′. As has been explained inmore detail in the context of the description of FIGS. 1 and 2, thethread brake 1 comprises a brake band 3 and a brake body 2 as well asadditionally a first electromagnet 6 and a rotatable or rocking lever 4which is in operationally connected to the brake band 3 in order to beable to exert a pulling force or a pressure in the longitudinaldirection of the brake band. In the second exemplary embodiment thelever 4 can be moved by means of the two electromagnets 6, 6′, with itbeing possible for example for the first one, e.g. as described above,to be used for the braking and the second one for the release of thebrake band, for example.

In FIG. 3A the thread brake 1 is shown during the braking; i.e. thefirst electromagnet 6 stretches the brake band 3 via the lever 4 so thatit lies in contact with the brake body 2, and the weft thread 10 isclamped between the brake band and the brake body. In the exemplaryembodiment which is shown in FIG. 3A, in contrast, the secondelectromagnet 6′ is switched off during the braking. The significance ofthe air gap between the first electromagnet 6 and the armature 5 wasalready discussed in the context of the description of the firstexemplary embodiment.

In an advantageous variant a part of the lever 4 is formed as anarmature 5, with it being possible for the two electromagnets to bearranged e.g. on oppositely disposed sides of the armature, with an airgap in each case between the electromagnet and the armature. Instead ofU-shaped cores or pot cores a magnetically conducting yoke can, forexample, also be provided on which two electromagnets are arranged, sothat the yoke forms a closed magnetic circuit with the electromagnets 6,6′ and the armature 5 with the exception of the air gaps.

FIG. 3B shows a side view of the exemplary embodiment which is shown inFIG. 3A with a released thread brake. The thread brake which is shown inFIG. 3B differs from that shown in FIG. 3A only through the excitationof the second electromagnet 6′ and the position of the lever 4 as wellas the state of the brake band 3. In FIG. 3B the second electromagnet 6′ventilates the brake band 3 via the lever 4, so that the brake band islifted off from the brake body 2 and the weft thread 10 can be ledthrough the gap between the brake band and the brake body withouthindrance, with the gap typically amounting to 1 to 2 mm. In contrast,the first electromagnet 6 is switched off in the exemplary embodimentwhich is shown in FIG. 3B during the release or venting of the threadbrake. An air gap can be provided between the second electromagnet 6′and the armature 5 during the release, but is not required in most casessince a regulation of the force during release can be dispensed with.

It is advantageous that the controlled thread brake for braking a weftthread in accordance with the present invention can be used on differentweaving machine types such as for example projectile and rapier weavingmachines and is in particular also suitable for rapidly running weavingmachines, since the paths travelled by the lever and the brake band canbe kept short and the thread brake reacts correspondingly quickly. It isfurthermore advantageous that the thread brake is also suitable for verycoarse yarns thanks to its large braking force range.

1. Controlled thread brake for braking a weft thread (10) in a weaving machine with a brake band (3) and a brake body (2), characterized in that the thread brake (1) includes an electromagnet (6, 6′) and a rotatable or rocking lever (4) which can be moved by means of the electromagnet and which is operationally connected to the brake band (3) in order to exert a pulling force in the longitudinal direction of the brake band and to place the latter against the brake body (2) for braking the weft thread.
 2. Thread brake in accordance with claim 1, with the thread brake comprising two or more brake bodies (2) and/or with the brake body or bodies (2) being formed as a passive brake element.
 3. Thread brake in accordance with claim 1, with the brake band (3) being firmly or elastically connected to a holder (8) at a first securing point, in particular at one end, and, spaced in the longitudinal direction, being firmly or elastically connected to the lever (4) at a second securing point, in particular at the other end.
 4. Thread brake in accordance with claims 1, comprising a spring element for the release of the thread brake, in particular a tension or compression spring, which acts on the lever (4) and/or a leg spring at the point of rotation of the lever and/or a prestressed brake band (3).
 5. Thread brake in accordance with claims 1, with the lever (4) being straight or angled, and/or with the lever (4) being arranged substantially at right angles to the brake band (3).
 6. Thread brake in accordance with claims 1, with the point of rotation of the lever (4) being arranged between the brake band (3) and the electromagnet (6) and/or one-sidedly on the side of the brake band or of the electromagnet.
 7. Thread brake in accordance with claims 1, with an armature (5) of the electromagnet (6, 6′) being provided at the lever (4), said armature containing a ferromagnetic or permanent magnetic material, and/or with the lever (4) or a part thereof being formed as an armature (5), and/or with the electromagnet (6, 6′) having a U-shaped core or being formed as a pot magnet and with the magnetic field passing through the armature (5).
 8. Thread brake in accordance with claims 1, comprising at least one second electromagnet (6′) by means of which the lever (4) and/or the brake band (3) can be moved and which is provided as a release magnet and/or to assist the first electromagnet (6).
 9. Thread brake in accordance with claims 1, with an air gap being provided between the armature (5) and the electromagnet or electromagnets (6, 6′) during the braking.
 10. Weaving machine comprising at least one thread brake in accordance with claims
 1. 